The present invention generally relates to the field of global positioning system (GPS) based navigation systems for ground vehicles, in particular agricultural ground vehicles such as tractors, combines, sprayers, cotton pickers, or the like, and more specifically, to a global positioning system based navigation system that is capable of providing inertial compensation for ground vehicle attitude as the ground vehicle traverses non-level or uneven terrain.
A shortcoming of global positioning system based navigation systems used in agricultural ground vehicles is that the global positioning system receiver of such systems can only determine the position of the global positioning system antenna. On most ground vehicles, the mounting location for the global positioning system antenna is constrained by the requirement that a clear view of the sky, and thus the global positioning system satellites, be provided to the antenna. Unfortunately, this position is usually not the desired control point (e.g., the hitch point of a tractor, the ground vehicle axle, a point on the ground beneath the hitch point of a tractor, or the like) for most ground vehicle applications. Consequently, when traversing non-level terrain (e.g., terrain having a slope, hills, valleys, or the like), the global positioning system determined position and course of the ground vehicle may be incorrect, resulting in cross-track and heading errors.
In order to calculate the position of the desired control point, a precise measurement of the spatial orientation (attitude) of the ground vehicle with respect to the navigation coordinate system must be made. One approach to measuring the attitude of the ground vehicle is to mount multiple global positioning system antennas to the vehicle in a fixed, known geometry. When precision global positioning system measurements are made, the relative positions of the multiple antennas, as measured in the navigation frame, can be used to calculate the orientation (position, attitude, and course) of the entire ground vehicle. However, a navigation system employing this approach would require multiple precision global positioning system receivers and would thus be prohibitively expensive.
Alternatively, an inertial system may be used in conjunction with the global positioning system. In this approach, the inertial system determines the primary position and course information for guiding or steering the ground vehicle. Information provided by the global positioning system is then used to correct drift of the position and course information determined by the inertial system. Inertial systems include gyroscopes for measuring roll, yaw and pitch, and may include accelerometers for improving the accuracy of the information measured by the gyroscopes. Consequently, such inertial systems, like multiple antenna systems, are prohibitively expensive for many applications
Accordingly, it would be desirable to provide a navigation system that employs inertial augmentation to compensate global positioning system based navigation information such as position, course, and track spacing for errors caused by variation of the ground vehicle attitude (i.e., roll and yaw) over non-level terrain, but which does not require the full suite of gyroscopes and accelerometers provided by a conventional inertial system.
The present invention is directed to a navigation system for a ground vehicle, in particular, an agricultural ground vehicle such as a tractor, combine, sprayer, cotton picker, or the like. The navigation system employs inertial augmentation to compensate global positioning system based navigation information such as position, course, track spacing, or the like, for errors caused by variation of ground vehicle attitude (i.e., roll and yaw) over non-level terrain. In this manner, the accuracy of the navigation system is increased without undue expense.
In accordance with a first aspect of the present invention, a navigation system for a ground vehicle is disclosed. In an exemplary embodiment, the navigation system includes a global positioning system receiver assembly for receiving a positioning signal from a global positioning system and generating navigation information including the position (e.g., latitude and longitude) and course of the ground vehicle and a navigation control system interconnected with the global positioning system receiver assembly to provide assisted steering of the ground vehicle. An inertial compensation assembly is coupled to the global positioning system receiver assembly and the navigation control system. The inertial compensation assembly replaces the position and course generated by the global positioning system receiver assembly with a corrected position and a corrected course that are inertially compensated for roll and yaw of the ground vehicle to provide corrected navigation information that is passed to the navigation control system, which uses the information for steering the ground vehicle. The inertial compensation assembly may further calculate the slope of the non-level terrain. The navigation control system may then use the slope to determine the effective track spacing of an implement associated with the ground vehicle (e.g., towed by the ground vehicle or mounted to the ground vehicle).
In accordance with a second aspect of the present invention, a method for steering a ground vehicle traversing non-level terrain is disclosed. In an exemplary embodiment, the method includes the steps of receiving a positioning signal from a global positioning system; generating navigation information for the ground vehicle, which includes a position and course for the ground vehicle; stripping the position and course from the generated navigation information; replacing the position and course stripped from the navigation information with a corrected position and a corrected course that are inertially compensated for roll and yaw of the ground vehicle for providing corrected navigation information; and steering the ground vehicle using the corrected navigation information. The method may further include the step of calculating the slope of non-level terrain traversed by the ground vehicle in order to determine the effective track spacing of an implement associated with the ground vehicle.
In accordance with a third aspect of the present invention, an inertial compensation assembly for a navigation system of a ground vehicle is disclosed. The inertial compensation assembly operates in cooperation with the navigation system""s global positioning system receiver assembly and steering assembly. In exemplary embodiments, the inertial compensation assembly comprises a gyroscope assembly for determining the yaw angle of the ground vehicle, an accelerometer assembly for determining the lateral acceleration of the ground vehicle, and a processing assembly. The processing assembly replaces the position and course information generated by the global positioning system receiver assembly with corrected position and course information that are inertially compensated for roll and yaw of the ground vehicle to provide corrected navigation information. The processor assembly generates the corrected position and course information using the yaw angle measured by the gyroscope assembly and the lateral acceleration measured by the accelerometer assembly so that the corrected navigation information is inertially compensated for roll and yaw of the ground vehicle over non-level terrain. The corrected navigation information is passed to the navigation control system, which uses the information for steering the ground vehicle. The processing assembly may further calculate the slope of the non-level terrain being traversed by the ground vehicle, allowing the effective track spacing of an implement associated with the ground vehicle to be determined.
In accordance with a fourth aspect of the present invention, a method for determining an effective track spacing for an implement associated with a ground vehicle traversing non-level terrain (e.g., towed by the ground vehicle or mounted to the ground vehicle) is disclosed. In exemplary embodiments, the method includes the steps of determining a roll angle for the ground vehicle; ascertaining the slope of the non-level terrain using the determined roll angle; and calculating the effective track spacing, wherein the effective track spacing compensates for the slope of the non-level terrain. The ground vehicle may then be steered using the corrected track spacing so that the ground vehicle follows a track substantially parallel and tangential to a previously navigated track. In this manner, cross-track error in positioning of the implement may be reduced or eliminated.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention.